N° 40–1999: ESA's Mercury mission named BepiColombo in honour of a space pioneer

30 September 1999

Meeting in Naples last week (20-23 September), the European Space Agency's Science Programme Committee recognised the achievements of the late Giuseppe Colombo of the University of Padua by adopting his name for the Mercury project now being planned. Almost everything known until now about the planet Mercury comes from three passes by NASA's Mariner 10 in 1974/75, which were inspired by Colombo's calculations. He suggested how to put that spacecraft into an orbit that would bring it back repeatedly to Mercury. The Italian scientist also explained, as an unsuspected resonance, Mercury's peculiar habit of rotating three times in every two revolutions of the Sun.

The mission to Mercury, now named after Prof. Colombo, is one of ESA's science programme "cornerstones". In the course of the comprehensive Horizon 2000 Plus review of the programme five years ago, it was identified by Europe's space scientists as one of the most challenging long-term planetary projects. Mercury is the least known of the inner planets. Its orbit close to the Sun makes it difficult to observe from a distance and hard to reach by spaceflight. As a result, big questions raised by the Mariner 10 flybys of a quarter of a century ago remain unanswered.

"I am very pleased we have given the name of BepiColombo to our Mercury cornerstone. Bepi was a great scientist, a great European and a great friend; we could do no better than name one of our most challenging and imaginative missions after him" said Roger Bonnet, Director of ESA Science Programme.

Scientists cannot claim to fully understand the origin and history of the Earth itself until they can make sense of Mercury. Why is the planet surprisingly dense ? Where does its magnetic field come from ? What were the effects of massive collisions suffered by Mercury, apparent in shattered zones seen by Mariner 10 ? Is Mercury geologically active ? How does its close proximity to the Sun affect its surface, its tenuous atmosphere and the small magnetic bubble, or magnetosphere, which surrounds it ?

BepiColombo will seek the answers to these and other questions with three separate sets of scientific instruments. According to preliminary studies completed in April 1999, a Planetary Orbiter will examine the planet from an orbit over the poles, using two cameras and half a dozen other remote-sensing instruments. Seven detectors in a smaller Magnetospheric Orbiter will observe Mercury's magnetic field and its interactions with the solar wind.

A Surface Element dropped by BepiColombo will land near one of the poles of Mercury, where the temperature is milder. Here the instruments will include a camera, a seismometer, a detector for chemical elements, and a package for assessing the temperature, heat capacity, density and hardness of Mercury's "soil". The Surface Element is expected to operate for at least a week and the two Orbiters for about 12 months. When ESA began contemplating a mission to Mercury, the journey time was expected to be nearly four years, with a complex series of manoeuvres around Venus and Mercury designed to bring the spacecraft into an orbit similar to Mercury's. Now BepiColombo's journey will be cut to about 2.5 years with the aid of a solar-electric propulsion module, which ejects heavy xenon ions at high speed to provide a small but continuous acceleration over many months. Swingbys of Venus and Mercury are still part of the mission profile, and a chemical propulsion module will finally put BepiColombo's main spacecraft into orbit around Mercury.

Personal notes about Prof. ColomboGiuseppe (Bepi) Colombo (1920-1984) was a mathematician and engineer of astonishing imagination, whose bald head and grey moustache were familiar in the corridors of both ESA and NASA. Apart from his work on Mercury, Colombo invented tethers for tying satellites together. As one of the initiators of ESA's mission to Halley's Comet he suggested its name, Giotto, but he died before that project was accomplished. At the University of Padua his work continues in CISAS, the Centro Interdipartimentale Studi ed Attività Spaziali "G. Colombo". In 1985 to commemorate this great scientist, ESA has created a "Colombo fellowship" to be granted to European scientists working in the fields of science explored by G.Colombo.